The present invention relates to an effective technology in being applied to a communication system in which a communication band necessary for a unit of terminal equipment can be secured by transmitting a call control message (SETUP message) to a network from the terminal equipment as in the case of a call procedure in B-ISDN, etc.
In the B-ISDN network, various terminal equipment is connected with one communication line through the Network Termination (NT). As for the kind of the terminal equipment, there are telephones, facsimiles, computer data terminals, video terminals, telex, etc. And it is possible to use some of these terminals at the same time.
In the B-ISDN Network, when the service is requested from the terminal, the communication starts after a network secures the communication band. For example, it is mentioned from column 3 line 47 to column 4 line 27 in U.S. Pat. No. 4,704,716 that a signal, i.e. SETUP message for requesting the width of the band is sent from a terminal, and then the network secures the adequate width of the band, and connects the communication line.
The width of the band to communicate depends on the kinds of the terminals. The terminal which contains much data requires the wide one, on the other hand, in the case of little data, it requires the narrow one.
When a SETUP message is transmitted to a network from a unit of terminal equipment, if a band setting in the network is found to be impossible according to the information element of the message, a call procedure has to be repeated. Because of this, it takes much time for the call process itself, so that it is felt a concern about the lowering off communication efficiency.